The XENON1T Data Distribution and Processing Scheme

The XENON experiment is looking for non-baryonic particle dark matter in the universe. The setup is a dual phase time projection chamber (TPC) filled with 3200 kg of ultra-pure liquid xenon. The setup is operated at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. We present a full overview of the computing scheme for data distribution and job management in XENON1T. The software package Rucio, which is developed by the ATLAS collaboration, facilitates data handling on Open Science Grid (OSG) and European Grid Infrastructure (EGI) storage systems. A tape copy at the Center for High Performance Computing (PDC) is managed by the Tivoli Storage Manager (TSM). Data reduction and Monte Carlo production are handled by CI Connect which is integrated into the OSG network. The job submission system connects resources at the EGI, OSG, SDSC's Comet, and the campus HPC resources for distributed computing. The previous success in the XENON1T computing scheme is also the starting point for its successor experiment XENONnT, which starts to take data in autumn 2019.Comment: 8 pages, 2 figures, CHEP 2018 proceeding

Removing krypton from xenon by cryogenic distillation to the ppq level

The XENON1T experiment aims for the direct detection of dark matter in a cryostat filled with 3.3 tons of liquid xenon. In order to achieve the desired sensitivity, the background induced by radioactive decays inside the detector has to be sufficiently low. One major contributor is the $\beta$-emitter $^{85}$Kr which is an intrinsic contamination of the xenon. For the XENON1T experiment a concentration of natural krypton in xenon $\rm{^{nat}}$Kr/Xe < 200 ppq (parts per quadrillion, 1 ppq = 10$^{-15}$ mol/mol) is required. In this work, the design of a novel cryogenic distillation column using the common McCabe-Thiele approach is described. The system demonstrated a krypton reduction factor of 6.4$\cdot$10$^5$ with thermodynamic stability at process speeds above 3 kg/h. The resulting concentration of $\rm{^{nat}}$Kr/Xe < 26 ppq is the lowest ever achieved, almost one order of magnitude below the requirements for XENON1T and even sufficient for future dark matter experiments using liquid xenon, such as XENONnT and DARWIN

On the krypton background of the Xenon100 and Xenon1T dark matter search experiments

The currently running Xenon100 experiment and its successor, Xenon1T, use liquid xenon as target and detection material in the search for weakly interacting massive particles, a well motivated candidate for dark matter in our universe. As the expected signal rate is less than a couple of events per year, it is absolutely mandatory to understand and reduce the possible background contributions. The man-made and almost pure beta-emitter 85Kr is a very dangerous background candidate, as krypton is intrinsically present on the ppb (parts per billion level b= 10−9) in commercially available xenon. Both further purification and the corresponding analytics are therefore equally important for these kind of experiments. This thesis describes two krypton in xenon measurement procedures and their impact on the understanding of the krypton background in the Xenon experiments. First, a mass spectroscopic set-up using gas-chromatographic pre-separation is introduced, and the improvements in terms of stability and sensitivity down to the ppq (parts per quadrillion b= 10−15) regime are highlighted. Subsequently several xenon assay results are presented: the evolution of the krypton concentration in Xenon100 over a time period of more than a year is reconstructed and linked to the observed radon decay rates. Furthermore, several distillation procedures are examined, showing the high potential of cryogenic distillation for xenon purification. Thereby, a measurement of ultra pure xenon with an so far unprecedented purity is presented. Finally, a second analysis method is investigated, applying a delayed coincidence analysis to the Xenon100 dark matter search data. This in-situ method is limited to the ppt (parts per trillion b= 10−12) regime, but achieves very good agreements with the mass spectroscopic results and confirms its absolute calibration

MonteCarlo simulation of the XENON1T experiment and first comparison with the Muon Veto data.

L’esperimento XENON1T, in acquisizione dati presso i Laboratori Nazionali del Gran Sasso, è una Time Projection Chamber (TPC) contenente 2 t di xeno liquido ed ha come obiettivo una sensibilità per sezioni d'urto WIMP-nucleone indipendenti dallo spin pari a 1.6 10^(-47) cm^(2), per WIMP di massa 50 GeV/c^(2), in 2 t y. A tale scopo è fondamentale la riduzione di tutte le sorgenti di fondo. Per abbattere il fondo esterno la TPC è inserita all'interno di un Muon Veto: una vasca cilindrica riempita di acqua, dotata di 84 fotomoltiplicatori (PMT) , che funge sia da schermo passivo contro la radiazione esterna (gamma e neutroni), sia da veto per i muoni grazie alla rivelazione della luce Cherenkov da essi prodotta in acqua. In questo lavoro presentiamo uno studio sulle configurazioni di trigger del Muon Veto e sulla sua efficienza. Lo studio è basato sul confronto di simulazioni Monte Carlo con i primi dati del rivelatore. Si ottiene un'efficienza del 99.5% per eventi di muone e del 43% per sciami generati da interazioni del muone nella roccia che circonda la sala sperimentale, e conseguente riduzione degli eventi di background attesi nell'attuale run scientifico a 1.3 10^(-3) eventi. È già previsto dalla collaborazione il futuro upgrade dell'esperimento: XENONnT. Uno studio sulle possibili geometrie della TPC di XENONnT è stato effettuato mediante simulazioni Monte Carlo. Tra le possibili migliorie apportabili a XENONnT vi è la sostituzione degli attuali sensori di luce con fotomoltiplicatori al silicio (SiPM). Le simulazioni mostrano che, mediante una copertura totale della TPC con i SiPM, si ha un aumento dell'efficienza nella collezione di luce (LCE) del 20%. La LCE è un parametro fondamentale per la rivelazione del segnale di luce (S1) nella TPC; in questa configurazione si raggiunge una soglia in energia per rinculi nucleari di circa 3 keV, aumentando in modo significativo la sensibilità dell'esperimento, in particolare per WIMP di piccola massa

Gravitational waves and electroweak baryogenesis in a global study of the extended scalar singlet model

We perform a global fit of the extended scalar singlet model with a fermionic dark matter (DM) candidate. Using the most up-to-date results from the $\mathit{Planck}$ measured DM relic density, direct detection limits from the XENON1T (2018) experiment, electroweak precision observables and Higgs searches at colliders, we constrain the 7-dimensional model parameter space. We also find regions in the model parameter space where a successful electroweak baryogenesis (EWBG) can be viable. This allows us to compute the gravitational wave (GW) signals arising from the phase transition, and discuss the potential discovery prospects of the model at current and future GW experiments. Our global fit places a strong upper $\mathit{and}$ lower limit on the second scalar mass, the fermion DM mass and the scalar-fermion DM coupling. In agreement with previous studies, we find that our model can simultaneously yield a strong first-order phase transition and saturate the observed DM abundance. More importantly, the GW spectra of viable points can often be within reach of future GW experiments such as LISA, DECIGO and BBO.Comment: 42 pages, 10 figures and 2 tables; v2: updated references, submitted to JHEP; v3: corrected typos and updated references, matches version published in JHE

Constraints on sneutrino dark matter from LHC Run 1

A mostly right-handed sneutrino as the lightest supersymmetric particle (LSP) is an interesting dark matter candidate, leading to LHC signatures which can be quite distinct from those of the conventional neutralino LSP. Using SModelSv1.0.1 for testing the model against the limits published by ATLAS and CMS in the context of so-called Simplified Model Spectra (SMS), we investigate to what extent the supersymmetry searches at Run 1 of the LHC constrain the sneutrino-LSP scenario. Moreover, we discuss the most relevant topologies for which no SMS results are provided by the experimental collaborations but which would allow to put more stringent constraints on sneutrino LSPs. These include, for instance, the mono-lepton signature which should be particularly interesting to consider at Run 2 of the LHC.Comment: 30 pages, 23 figures, matches published versio